1. Field of the Invention
This invention relates to a locomotion control system for a mobile robot and more particularly to a system in which mobile robot is controlled to move at a high speed while keeping its posture in an environment such as stairs in which its motion is restricted.
2. Description of the Prior Art
Wheeled, crawler, legged or other types of mobile robots have been proposed. Among the numerous reports published regarding control technologies for the legged mobile robot includes some relating to the one-legged robot (Raibert, M. H., Brown, Jr. H. B., "Experiments in Balance with a 2D One-Legged Hopping Machine", ASME, J of DSMC, vol. 106, pp. 75-81 (1984)), the two-legged robot (J of the Robotic Society of Japan, vol.1, no. 3, pp. 167-203 (1983)), the four-legged robot (J of the Robotic society of Japan, vol. 9, no.5, pp. 638-648 (1991)), and the six-legged robot (Fischeti, M. A., "Robots Do the Dirty Work", IEEE, Spectrum, vol. 22, no.4, pp. 65-72 (1985) and Shin-Min Song, Kenneth J. Waldron, "Machines That Walk; The Adaptive Suspension Vehicle", The MIT Press Cambridge, Mass. Other reports have been published regarding techniques for real time generation of dynamically stable gait parameters for a robot with relatively few degrees of freedom (Shimoyama, "Dynamic Walking of Stilt-type Biped Walking Robot", Collected Papers of The Japan Society of Mechanical Engineers, book C, vol.48, no.433, 1445-1454 (1982) and "Legged Robots on Rough Terrain; Experiments in Adjusting Step Length", by Jessica Hodgins, IEEE (1988)), and also on techniques for offline generation of stable gait parameters for a robot with relatively many degrees of freedom (Japanese Laid-Open Patent Publication nos. 62(1987)-97006 and 63(1988)-150176). Also the assignee proposed the anthropoid biped robot in Japanese Patent Application No. 2(1990)-336,420 (Laid-open Patent Publication No. 4(1992)-201,187) etc.
Among them, a robot such as a legged mobile robot moves around discretely bringing its foot in contact with a floor. It is therefore necessary, when the robot moves around in an environment such as stairs in which floor contact position is restricted, that the robot foot is landed at a desired position. More specifically, when a biped robot goes up stairs as illustrated in FIG. 13, if the robot lands its foot on a stair at a position excessively behind that desired, contact area between the stair and the foot sole necessary for keeping its posture stable is so small that the robot loses its stability. On the other hand, if the robot places its foot at a position excessively before that desired, the free (swung) leg may interfere with the next stair, causing the robot loses its stability. Thus, when such a robot walks around in the environment in which its motion, i.e., floor contact position is restricted, it is necessary to control the relative positional relationship between the robot contact portion and the floor (stair).
In this respect, there have been proposed two techniques concerning foot landing control. In the first technique, the robot is provided at its foot end with a noncontact proximity sensor and the sensor outputs are successively processed to grope for a position to be landed. Namely, a foot landing position is felt with a free leg. In the second technique, a robot is controlled using modern control theory or the like in such a manner that its leg's vibration is suppressed so that the robot walks with a desired stride. It can be concluded that the two techniques aim to prevent a relative positional error between the robot foot and the floor (stair) from occurring. However, the first technique is disadvantageous in that the robot's walking speed is degraded, since it takes a considerable time for looking for a foot landing position. The second technique is disadvantageous in that it requires a high performance computer, resulting in complex structure and herece is expensive.
The object of the invention is therefore to provide a locomotion control system for a mobile robot in which the robot is able to stably move at a relatively high speed even in an environment such as stairs in which its motion is restricted.
Another object of the invention is therefore to provide a locomotion control system for a mobile robot in which the structure of the system is relatively simple and hence less expensive.